Yes, William is right. If you're just serving them up as static files, there is no need to stream them.
In Tomcat, mime types are set up in the global web.xml file located under TOMCAT_HOME/conf.
We've had a lot of people asking how to serve up dynamic content as Excel and
Word files this week and conequently, I skimmed your post and jumped to the wrong conclusion.
Sorry about that.
-Ben